Pointer-type measuring units, i.e., measuring units with a rotating pointer as the indicating member, are arranged in mounting housings of this class such that the pointer of the measuring unit sweeps over a ring dial or circular dial, which is arranged on the front side of the flange ring and, depending on the design of the measuring instrument, it may have a larger or smaller diameter, to which the length of the pointer is also adapted.
In the prior-art mounting housings of this class, the flange rings are made in one piece with the essentially cylindrical housing boxes on the front side, so that the cylindrical box wall ends at the flange ring, on the one hand, and at the housing bottom, on the other hand, and it is therefore completely inelastic in the radial direction at least at the two ends. It is therefore also necessary to arrange the deflectable snap-in elements, especially ratchet teeth, on elastic tongues, which are movable in relation to the housing wall. These tongues may be made in one piece with the bottom of the housing box inside the housing box, but they may also be grooved or cut loosely by three-sided slitting in the area of the box wall, so that they are also able to move elastically in relation to the box wall in the radial direction. Aside from the fact that such tongues preserve the elasticity of movement even when the ratchet teeth fastened to them engage the parts of the measuring unit which are to be held and thus there is a relatively great risk of unintended spontaneous detachment, there have also been efforts to design such mounting housings such that different pointer-type measuring units, e.g., thermometers, barometers, hygrometers, and the like, can be optionally inserted. In addition, the same pointer-type measuring units are provided with pointers of different length or with ring dials with different diameters, so that a fitting, complete mounting housing must also be available for each ring dial with a defined diameter in the case of the prior-art mounting housings, even though the measuring unit itself and the housing box accommodating it could always have the same shape.